Inertial navigation system error correction

Abstract

Methods and apparatus for: (a) the correction of one or more elements determined from a first set of continuous gyro and accelerometer measurements comprising using a second set of discontinuously measured higher accuracy accelerometer measurements doubly integrated in an inertial coordinate system, (b) determining relative movement of a vehicle using a first set of acceleration measurements that do not include components of acceleration caused by the Earth's gravitational field, and a second set of acceleration measurements that do include components of acceleration caused by the Earth's gravitational field; and (c) correcting errors in an inertial navigation system positioned in a vehicle comprising using independently measured changes in position of the vehicle relative to an inertial coordinate frame.

1. A method of correcting error state vector of a first inertial navigation system with a change in position measurement from a second measurement system, comprising:
 continuously acquiring a first set of gyro and accelerometer measurements having inertial instrument errors and computed navigation errors; 
 discontinuously acquiring, during periods of availability, a second set of acceleration measurements of higher accuracy than the first set of gyro and accelerometer measurements; 
 synchronously doubly integrating the first set of measurements and the second set of measurements during a period of availability to obtain, respectively, a first change in position measurement and a second change in position measurement; 
 comparing the first change in position measurement to the second change in position measurement to obtain a Kalman observable; and 
 correcting the first set of gyro and accelerometer inertial instrument errors and computed navigation errors using the Kalman observable. 
 
     
     
       2. The method of  claim 1  wherein the second set of acceleration measurements is obtained from a measurement system external to a vehicle on board which the first set of continuous gyro and accelerometer measurements are performed. 
     
     
       3. The method of  claim 2  wherein the measurement system is a global positioning system. 
     
     
       4. The method of  claim 1  wherein both the first and second sets of measurements are performed on board a common vehicle. 
     
     
       5. The method of  claim 1  wherein the computed navigation errors include errors in variables representing at least one of position, velocity, and orientation with respect to Earth. 
     
     
       6. The method of  claim 1  wherein the correcting step further comprises correcting errors in the second set of acceleration measurements using the Kalman observable. 
     
     
       7. The method of  claim 1  wherein the integrating step further comprises synchronously doubly integrating the first and second sets of measurements over an identical time period within the period of availability. 
     
     
       8. The method of  claim 1  wherein the second set of acceleration measurements are discontinuously acquired from strapdown accelerometers.